This invention relates to a two cycle diesel engine and more particularly to a two cycle diesel engine and a method of operating it that will reduce the nitrous oxide emissions, particularly at low and mid ranges.
The fuel efficiency of diesel engines is well known. This fuel efficiency is achieved through the use of high compression ratios and thus the possibility to extract a greater amount of thermal energy from the burning of the fuel than engines running on lower compression ratios. However, although the fuel efficiency of an engine operating on the diesel cycle can be improved over that of one operating on the Otto cycle, there are certain other problems in connection with diesel engines.
Specifically, a diesel engine, because of its higher combustion chamber pressures and temperatures, is likely to present greater problems in connection with nitrous oxide (NOx) emissions than spark ignited engines. If the engine is operated in such a manner that the NOx emissions are reduced, there may be a problem with hydrocarbon, carbon particles or carbon monoxide in the exhaust gases. These problems are particularly acute when running at low or mid ranges. In addition, a characteristic similar to the knocking of a spark ignited engine is frequently a problem with diesel engines due to the high compression ratios, compression pressures and combustion system temperature.
It is, therefore, a principal object of this invention to provide an improved diesel engine and method for running it wherein the nitrous oxide emissions can be more adequately controlled.
It is further object of this invention to provide an improved arrangement for a diesel engine that will reduce the nitrous oxide emissions and combustion chamber temperatures at low and mid range performance.
In connection with diesel engines and particularly two cycle crankcase compression diesel engines, it has been proposed to employ an exhaust control valve which is effective to provide an increase in compression ratio of the engine under certain running conditions. Normally, this increased compression ratio is provided at low and mid range performances to improve efficiency and avoid the likelihood of knocking when running at high loads and high speed conditions. However, such increased compression ratio further aggravates the nitrous oxide problems aforementioned.
It is a further object of this invention to provide a two cycle crankcase compression diesel engine operating on variable compression ratio and wherein combustion chamber temperatures are lowered at low and mid range performance to reduce the likelihood of nitrous oxide emissions.